Olefin polymers, such as polyethylene, linear low-density polyethylene (LLDPE) which is a copolymer of ethylene and an .alpha.-olefin and an ethylene/propylene terpolymer (EPT), are widely used as film forming materials and industrial materials.
The olefin polymers are produced using Ziegler catalysts or metallocene catalysts. By virtue of recent improvements of transition metal catalysts for olefin polymerization, production capacity of an olefin polymer per unit quantity of the transition metal has been rapidly increased, and as a result, catalyst removal operation after the polymerization came to be omitted.
In particular, the metallocene catalysts are highly active and are known to exhibit excellent mechanical properties of the resulting polymer such as high transparency and surface non-tackiness because of narrow molecular weight distribution. Therefore, the catalysts are coming to be practically used in solution polymerization, slurry polymerization and gas phase polymerization.
When the metallocene catalyst is used as a solid catalyst for the slurry polymerization or the gas phase polymerization, there has been made an attempt to conduct olefin polymerization in a slurry polymerization system or a gas phase polymerization system using an inorganic carrier supported type solid catalyst wherein any one or both of a metallocene catalyst component and an aluminoxane are supported on a porous inorganic oxide carrier such as silica, silica/alumina or alumina.
However, if an olefin is polymerized or copolymerized in a slurry polymerization system or a gas phase polymerization system using the inorganic carrier supported type solid catalyst, the activity per unit weight of the catalyst becomes lower than that in the solution polymerization system, because silica or the like making no contribution to the activity is contained in the catalyst.
In the polymerization of an olefin using the inorganic carrier supported type solid catalyst, further, a polymer having a relatively high bulk density is obtained. In the gas phase polymerization or the slurry polymerization, polymerization is generally carried out in a state such that a polymer is present around the active site, differently from the solution polymerization. Hence, an ununiform polymer having a wide composition distribution and/or a wide molecular weight distribution is apt to be obtained. Especially in case of polymer particles hardly having voids in the particles, distribution of monomer concentration easily takes place because of low monomer diffusion into particles, whereby an ununiform polymer is apt to be obtained.
Moreover, in the preparation of a prepolymerized catalyst, prepolymerized catalyst particles occasionally adhere to each other or to a wall of the polymerization reactor.